1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus which jets liquid droplets.
2. Description of the Related Art
A color ink-jet printer which carries out recording of an image by jetting droplets of inks of a plurality of colors on to a recording medium has hitherto been known as a liquid droplet jetting apparatus which jets liquid droplets from nozzles. In the ink-jet printer, due to an increase in a viscosity (hereinafter, also called as “thickening”) of ink in the nozzle due to drying, and due to an entry of dust or an air bubble into an ink channel communicating with the nozzle, a jetting defect is susceptible to occur in the nozzle. Therefore, in a normal inkjet printer, it is possible to perform a so-called purge operation, in which the ink is discharged forcibly from the nozzle, and the thickened ink and the air bubble which cause the jetting defect are removed with the ink.
For instance, a conventional ink-jet printer disclosed in U.S. Pat. No. 7,121,644 (corresponding to Japanese Patent Application Laid-open No. 2005-14368) includes a carriage which is reciprocatable in a width direction of a paper which is a recording medium, four ink cartridges which store inks of four colors respectively, and which are attached to the carriage, and an ink-jet head which is attached to the carriage, and which has four nozzle rows jetting the inks of four colors. Moreover, the conventional ink-jet printer includes a purge unit which is provided at a predetermined purge position, and which carries out the purge operation. The purge unit includes four suction caps which cover liquid droplet jetting ports of the nozzles (four nozzle rows) of four colors by making a close contact with the ink-jet head when the ink-jet head has moved to the purge position, and a suction pump which is connected to the suction caps. The ink is discharged by sucking from the nozzles (suction purge) by generating a negative pressure inside the suction caps by the suction pump, in a state of the nozzles for four colors covered by the suction caps.
In such inkjet printer, for example, by attaching an ink supply port sealing cap instead of an ink cartridge of a specific color (for example, an ink cartridge which stores a color ink), ink supply port which supplies an ink of the specific color to the ink-jet head is blocked, and it is possible to perform printing of an image etc. by using only inks (such as black ink) other than the ink of that specific color.
In such conventional ink-jet printer, when one suction pump is connected to four suction caps covering the four nozzle rows corresponding to the inks of four colors respectively, only by operating one suction pump with the four nozzle rows covered by the suction caps respectively, it is possible to perform the suction purge at a time for all the nozzles. In other words, it is possible to perform the suction purge efficiently for all the nozzles at the same time.
Incidentally, in such conventional ink-jet printer, as it has been described above, for making an arrangement such that certain specific color is not used, sometimes the ink supply port sealing cap is attached to the carriage instead of the ink cartridge for the ink of that specific color. In this manner, in a state of the ink of the specific color not supplied to the ink-jet head, when the suction pump is operated after covering the nozzles by the suction cap in the same manner as described above, naturally, the ink is discharged from the nozzle which jets the ink of the specific color, and the suction purge is performed only for the nozzles which jet the inks of colors other than the specific color.
However, when the suction pump is operated, in a case, in which the suction purge is performed for all types of nozzles (hereinafter, also called as a “complete purge”), and in a case, in which ink channels communicating with a part of the nozzles are closed, and the suction purge is performed only for the rest of the nozzles (hereinafter, also called as a “partial purge”), the number of nozzles from which the ink is discharged practically differs. Therefore, when suction conditions (such as a suction speed and a suction amount are not changed, a flow speed and an amount of the ink discharged from each nozzle differ. Therefore, there is a possibility that the purge from a certain nozzle is insufficient, and the jetting defect cannot be eliminated, or there is a possibility that an excessive ink surpassing substantially an amount necessary for eliminating the jetting defect is discharged.